--- /dev/null	2018-04-03 12:55:20.301839954 +0200
+++ new/src/hotspot/share/gc/z/zMetronome.cpp	2018-06-01 22:30:48.105204418 +0200
@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+#include "precompiled.hpp"
+#include "gc/z/zMetronome.hpp"
+#include "runtime/mutexLocker.hpp"
+#include "runtime/timer.hpp"
+#include "utilities/ticks.hpp"
+
+ZMetronome::ZMetronome(uint64_t hz) :
+    _monitor(Monitor::leaf, "ZMetronome", false, Monitor::_safepoint_check_never),
+    _interval_ms(MILLIUNITS / hz),
+    _start_ms(0),
+    _nticks(0),
+    _stopped(false) {}
+
+uint64_t ZMetronome::nticks() const {
+  return _nticks;
+}
+
+bool ZMetronome::wait_for_tick() {
+  if (_nticks++ == 0) {
+    // First tick, set start time
+    const Ticks now = Ticks::now();
+    _start_ms = TimeHelper::counter_to_millis(now.value());
+  }
+
+  for (;;) {
+    // We might wake up spuriously from wait, so always recalculate
+    // the timeout after a wakeup to see if we need to wait again.
+    const Ticks now = Ticks::now();
+    const uint64_t now_ms = TimeHelper::counter_to_millis(now.value());
+    const uint64_t next_ms = _start_ms + (_interval_ms * _nticks);
+    const int64_t timeout_ms = next_ms - now_ms;
+
+    MonitorLockerEx ml(&_monitor, Monitor::_no_safepoint_check_flag);
+    if (!_stopped && timeout_ms > 0) {
+      // Wait
+      ml.wait(Monitor::_no_safepoint_check_flag, timeout_ms);
+    } else {
+      // Tick
+      return !_stopped;
+    }
+  }
+}
+
+void ZMetronome::stop() {
+  MonitorLockerEx ml(&_monitor, Monitor::_no_safepoint_check_flag);
+  _stopped = true;
+  ml.notify();
+}